| Cucumber (Cucumis sativus L.) is one of the main vegetables cultivated in greenhouse, playing an important role in vegetable production and daily consumption. Being sensitive to temperature, cucumber often suffers to temperature stress easily. Due to the simply facilitated greenhouse in China which control its inner temperature inefficiently and the appeal for reducing carbon emission from domestic and abroad in recent years, temperature stress will continually be one of the main factors which threaten the greenhouse production of our country in future. Therefore, studying the mechanisms and increasing cucumber tolerance to temperature stress will help in stabilizing vegetable production and supply for our country. In this thesis, using Cucumis sativus L. cv. Jinyan No.4 as the material, we analyzed the effect of different temperatures to growth development and related physiological processes, and investigated the influence of H2O2 in regulating temperature acclimation of cucumber photosynthetic system as well. The main results were obtained as follows:1. We studied the impact of different temperatures on cucumber photosynthesis, cell devision, expansion and related genes expression. After treating seedlings in 11/9, 18/15,25/20,32/27 and 39/33℃for 24 h, we determined its photosynthesis and calvin cycle related enzymes activity, and analysed nuclear DNA content in leaf by flow cytometry as well. As results indicated,11/9 or 18/15℃treatment significantly inhibited net photosynthesis (Pn) and the lower the temperature, the more significant the inhition. Compared with Pn, the effect of chilling to Fv/Fm was much weaker, only Fv/Fm underll/9℃reduced significantly. In addition, chilling decreased Rubisco, PGK and GAPDH activity significantly, while 39/33℃inhibited the activity of Rubisco and PGK. To investigate the effects of different temperature on leaf cell division, we analyzed leaf nuclear DNA content by flow cytometry and detected the response of genes expression in cell cycle and cell expansion. Data indicated that high or low temperature inhibited cell cycle progression, resulting in the decrease in 4C/2C value; 11/9 and 18/15℃inhibited genes expression of cell cycle and expansion, but 32/27 and 39/33℃improved cell cycle gene expression, only 39/33℃had positive effect on cell expansion related genes. Additionally, our results also showed the response of GSH/GSSG value to temperature was highly lineared with those parameters mentioned above.2. We investigated the effects of different temperature treatments during seedling period on sequential cucumber growth and photosynthesis under differdent temperatures. We first put seedlings with only cotyledons into 17/11 and 34/23℃(day/night average temperature); when cucumber arrived the stage with three leaves, we put them into five different temperatures (11/9,18/15,25/20,32/27 and 39/33℃). After 10 days treatment, we determined photosynthesis, calvin cycle related enzymes (Rubisco,FBPase,PGK and GAPDH) activities, contents of H2O2 and MDA, and biomass as well. The data showed that, when transferred to 11/9 or 18/15℃, compared with that of 34/23℃, plants grown under 17/11℃had decreased contents of H2O2 and MDA, indicating low temperature acclimation enhanced resistance to chilling; this also happened when 34/23℃grown seedlings moved to 32/27 or 39/33℃. Cucumber grown under 34/23℃had its maximum activities of Rubisco, FBPase, PGK and GAPDH under 32/2℃, which brought up the highest maximum photosynthesis (Pmax) and the highest biomass accumulation under 32/27℃. In summary, when the temperature during seedling period increased, the most suitable temperature for cucumber growth shifted from 25/20℃to 32/27℃.3. We studied the role of H2O2 in regulating temperature acclimation of cucumber photosynthetic system. After treating plants pretreated with H2O2 or its scanvager DMTU with 11/9,18/15,25/20,32/27 and 39/33℃for ten days, H2O2 treatment promoted cucumber growth, enhanced photosynthesis, and improved the activities of Rubisco, FBPase, PGK and GAPDH under all of the five temperatures as well, while DMTU treatment effected adversely. Therefore, we hypothesized H2O2 or DMTU treatment might influence photosynthesis through influencing those enzymes activities, thus promoting or inhibiting cucumber growth finally.
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